Atrial fibrillation is the most common form of heart arrhythmia. In a normally functioning heart, an electrical system directs electrical impulses through the heart in an organized fashion to stimulate the heart so that it properly contracts. Specifically, the upper chambers (atria) and the lower chambers (ventricles) of the heart are stimulated to contract in a synchronous manner. Fundamentally, atrial fibrillation is the loss of synchronicity between the upper chambers and the lower chambers of the heart. In effect, atrial fibrillation is a very fast, uncontrolled heart rhythm in which the atria quiver instead of beating. Atrial fibrillation can be described as a storm of electrical energy that travels across both atria causing them to fibrillate at 300 to 600 times a minute. This storm of electrical energy interferes with the electrical system of the heart and prevents the heart from functioning properly.
Research has shown that almost all atrial fibrillation occurs at the ostium of the pulmonary veins at the left ventricle of the heart. Specifically, atrial fibrillation is the result of abnormal electrical signals that pass through the pulmonary vein openings and enter the heart. Inside the heart, these abnormal electrical signals can disrupt the electrical system and cause the heart to beat abnormally. Accordingly, preventing the abnormal electrical signals from reaching the heart is one method for treating atrial fibrillation. In one such treatment method, the ostium of the pulmonary veins are circumferentially ablated to destroy tissue around the periphery of the ostium. Consequently, the destroyed tissue is no longer able to initiate or conduct any type of electrical signal. Accordingly, abnormal electrical signals are prevented from reaching the heart through the pulmonary veins.
One technique for ablating the tissue around the ostium of the pulmonary veins involves cryoablating the tissue with a cryoablation catheter. In this technique, the cryotip of the cryoablation catheter is repeatedly contacted with tissue around the periphery of the ostium to cryoablate the tissue in a piecemeal fashion. Ideally, the cryoablated tissue is destroyed to form a uniform and continuous circumferential lesion around the periphery of the ostium. If properly formed, the lesion will not conduct electrical signals that may cause atrial fibrillation. In some instances, however, this procedure may result in a non-uniform or discontinuous circumferential lesion that does not adequately block the abnormal electrical signals. This occurs because it is difficult to form a uniform and continuous circumferential lesion with successive cryoablations that are performed in a piecemeal fashion. Specifically, the cryotip of the catheter must be repeatedly and accurately positioned around the periphery of the ostium to properly form the circumferential lesion. Moreover, this procedure is time consuming because it requires extensive manipulation of the cryotip around the ostium.
In light of the above, it is an object of the present invention to provide a device and method for performing single-step cryoablation of circumferential tissue in the vasculature of a patient. Another object of the present invention is to provide a device and method for cryoablating peripheral tissue around the ostium of a pulmonary vein to treat atrial fibrillation. Still another objection of the present invention is to provide a device and method for cryoablating circumferential tissue in the vasculature of a patient in an efficient and reliable manner.